1. Field of the Invention
The invention relates to an apparatus and a method for irrigating areas of ground according to requirements as provided by preamble of the independent patent claims.
2. Description of Related Art
The irrigation of areas of ground according to requirements, in particular areas of grass or areas under cultivation, is increasingly gaining in significance, since water demand is a very important economic factor—especially in critical climatic zones. Therefore, a series of methods have been developed to adapt the water input to the requirement of the plants. Apart from the evaluation of weather data and resultant predictions of the irrigating period, soil moisture sensors are also known, sensors which electronically measure the moisture in the soil and determine the irrigating time and/or the irrigating period by the aid of a control circuit, as described for example in WO 2007/059 636.
With such stationary sensors, measuring is performed at discrete points. Correspondingly, the results achieved with these methods are all the better the more uniform the soils to be irrigated are and the more uniform exposure to the sun is. This is the case, for example, with unroofed sports facilities. In other applications, such as soils left to nature in gardens, parks or agriculturally exploited soils, this condition is not satisfied. The composition of the soils, and consequently also the water storage capacity (field capacity), may vary very greatly. The form of terrain also plays an important part, since the water can flow off more quickly on slopes than in shallow depressions. Moreover, there are areas which may, for example, be shaded by buildings or trees, while other areas are fully exposed to the sun. In such cases, the areas must be divided up and assigned their own soil moisture sensors, so that the irrigation can be controlled in accordance with the needs of these zones. In this way it is already possible to achieve a reduction in water consumption of up to 30%.
A further influencing factor in minimizing the amount of water is the uniformity of the water distribution that can be achieved by an irrigating apparatus, such as for example a sprinkler. This is typically in the range of +/−50%, i.e. irrigation must always be continued much longer to the areas that are undersupplied. In this way, however, the other areas passed over are oversupplied, i.e. water is wasted. The larger the area intended to be covered by the sprinkler, the poorer the uniformity of the water input will turn out to be. In addition to this there is the influence of wind, which can blow the water about considerably, and the influence of solar irradiation and heat, under which some of the water evaporates before it reaches the ground.
For example, golf courses have a very high water consumption, and correspondingly high water costs. They reportedly have annual water consumption amounts of between 100,000 and 300,000 m3 of water. Moreover, investment costs and maintenance costs for the irrigation infrastructure are very high. The structure of the soil is generally very homogeneous—since it has been artificially laid. Even so, golf courses also have shaded areas or slopes where the water can flow off quickly.
For the reasons mentioned, it would be desirable to use an irrigation technique which could determine the current water requirement at every desired point of the area to be irrigated. Moreover, there is the requirement for a water distributing technique which on the one hand ensures a uniform distribution and at the same time prevents unnecessary delivery or evaporation of water. Furthermore, not only with respect to the investment but also in operation and maintenance, such a technology should be as low-cost as possible.